Magnetrons



' R. DUNSMUIR MAGNETRONS March 22, 1960 2 Sheets-Sheet 1 Filed Feb. 13,1959 //V l/E' N TOR fPOEff/FT 00 IF? 147' TOFPNEY March 22, 1960 R.DUNSMUIR MAGNETRONS 2 Sheets-Sheet 2 Filed Feb. 13, 1959 Claimspriority, application Great Britain February 13, 1958 2 Claims. (Cl.BIS-39.75)

.This invention relates to ultra-high frequency electron dischargedevices. It has application in travelling wave amplifiers, oscillatorsand accelerators, including both magnetron and other types.

Magnetron oscillators in which alternate segments are strapped togetherby means of conductive connecting links are well known. Although theseconnecting links are substantially straight they nevertheless provide ameasure of inductive coupling between the resonators. With such a formof coupling the dispersion curve, which is defined as the relationshipbetween phase shift ,9 and frequency w is such that the group velocity Bmay be opposite in direction to the phase velocity Although this is ofno consequence for magnetron oscillators it is unsuitable for magnetronamplifiers, where both phase and group velocity should preferably havethe same direction.

It is an object of the present invention to ensure that the groupvelocity has the same direction as the phase velocity in the fundamentalmode, throughout an appropriate frequency range.

Accordingly the present invention comprises an ultrahigh frequencyelectron discharge device having resonant cavities formed by a pluralityof slotted laminae stacked so that the slots in successive laminae arealigned to define resonant cavities and wherein the slots in differentlaminae are so shaped that portions of slots defining adjacent cavitiesoverlap, whereby mutual inductive coupling is obtained betweensuccessive resonant cavities.

The circuit may be in any one of several forms. It may form a completering, a portion of a ring or it may be straight and the invention isapplicable to all these possible constructions.

It is important for the satisfactory operation of the device, that theinterlaminar spaces should be of such a size that they do not resonateat any frequency within the pass-band of the device.

In a particular arrangement the anode block is composed of two annulidisposed coaxially. Each annulus has a number of slots opening into itsinner periphery and forming segments between them. The correspondingsegments of the two annuli are connected together to form completesegments extending along the whole axial length of the block, theconnection being made near to the inner periphery. It is arranged thatthe inductance of the connecting portions is low compared with that of aslot. The unslotted edges of the annuli may also be connected togetherat the outer periphery. The slots are so shaped and the annuli soassembled with respect to each other that part of the inductive regionof any slot on one side of a particular segment in one annulus iscontiguous with a "ateint similar inductive region of a slot on'theother side of the same segment in the other annulus. Itwill beappreciated that with such an arrangement mutual inductive coupling isprovided between adjacent resonant cavities.

In order that the invention may be more fully understood reference willnow be made to the accompanying drawings,in which: p

Fig. l and Fig. 2 show linearly developed views of laminae suitable forthe invention; I

Fig. 3 shows a linearly developed view of these laminae superimposed oneach other to form an anode block;

Fig. 4 shows a desired dispersion curve of a device :in accordance withthe invention; and p I N Fig. 5 is aplan sectional view, taken alongline 5 5 of Fig. '6, illustrating a magnetron embodying the presentinvention; and

Fig. 6 is an elevational sectional view, taken along line 6-6 of Fig. 5.

Referring to Fig. 1 there is shown therein a lamina 1 having a pluralityof slots such as 2. Slot 2 contains an entry portion 3 symmetricallydisposed about a radial line bisecting the gap between adjacent segmenttips 4 and 5 and an asymmetrically disposed end portion 6 of the slot.It now such a lamina is turned over it will appear as shown in Fig. 2 inwhich like parts have like reference numerals with a bar (1). Here endturns 6 of the slots are now on the opposite side of a radial linebisecting a slot. To construct an anode block the lamina 1 of Fig. 1 andlamina 1 of Fig. 2 are superimposed one on the other as shown in Fig. 3and are connected together at or near the inner tips of the segments. Ifdesired the laminae may also be connected at their outer peripheries soas to form a more stable structure. It will be seen that with such anarrangement the end portions 6 of the lamina of Fig. 1 will overlap theend portion 6' of the lamina of Fig. 2 so as to provide mutual inductivecoupling between successive resonant cavities defined by the entryportions 3 and 3 of the slots.

When excited in the pi-mode, for which the magnetic flux tends to flowinstantaneously in opposite directions in adjacent resonators, the fluxassociated with the mutual inductance opposes that associated with theself inductance. This is alternatively described by noting that the fluxassociated with current flowing around a given resonator opposes theflux due to current flowing simultaneously in the coupled resonators.When excited in the zero mode, in which the currents flow in the samedirection round all the resonators, the fluxes in a given resona torassociated with self and mutual induction flow in the same direction. Itfollows that the stored magnetic energy per unit is lower for thepi-mode than for the zero mode and consequently the pi-mode resonantfrequency is higher than that of the zero mode. By reference to theresulting dispersion curve shown in Fig. 4 it is clear that the groupvelocity for the fundamental component is in the same direction as thephase velocity.

It will be appreciated that more than two laminations could be used, andif desired they could be inverted a1 ternately or in packets, and itwill be realised that the coupling could be modified by making thenumber of laminations of one hand diflerent from the number .oflaminations of the other hand.

Figs. 5 and 6 illustrate a magnetron embodying the present invention.This magnetron is of a conventional type, such as the general typedisclosed in Principles and Practice of Radar, Penrose and Boulding, 6thed. (1958), page 282, 283, and 284, except for the features of thepresent invention, and comprises an annular anode 7 constructed of aplurality of slotted laminations 1 shaped as illustrated in Fig. l andFig. 2 and stacked together in the manner illustrated in Fig. 3. Themagnetron is sealed by two cover plates 10 and 11 placed at each end. Acathode 8, heated by a heater 9, emits electrons which are re pelled bya repeller electrode 15 to form a beam which traverses the annular spacebetween anode 7 andsole plate 16 along the path indicated by dotted line12 until they reach vcollector electrode 17. The input to the magnetronis provided by an input coupling loop 18 provided in the first cavityand the output from the magnetron is taken from an output coupling 19provided in the last cavity. It will be appreciated that the magnetronillustrated in Fig. 5 and Fig. 6 will be placed between the poles of amagnet which provides a magnetic field extending axially of themagnetron.

What I claim is:

1. An ultra-high frequency electron discharge device including aplurality of walls defining cavities between the walls, said walls beingformed by a stack of slotted laminae, the slots of each lamina having anentry portion and an end portion, the entry portions of the slots ofeach lamina being aligned with the entry portions of the correspondingslots of all the other laminae and the end portionsof each lamina beingaligned with the end portions of some only of the other laminae.

2. A magnetron including an anode block comprising two coaxial annulieachhaving a plurality of slots extending radially outwards from theinner periphery of the annuli, the entry portion of the slots of bothannuli being aligned with each other and the end portion of the slots ofeach annulus extending in respective opposite directions and overlappingthe end portions of the adjacent slot of the other annulus.

References Cited in the file of this patent UNITED STATES PATENTS2,583,793 Nelson Jan. 29, 1952 2,606,307 Pease et a]. Aug. 5, 19522,817,789- Steirnel Dec. 24, 1957

